Infants with birthweights between 401 and 1000 grams who were born between January 1, 1993, and October 31, 1994, cared for in the Newborn Special Care Unit and survived to hospital discharge were retrospectively located and evaluated with a battery of developmental tests at 18 to 22 months of age. Since November 1994, infants with birthweights between 401 to 10000 grams who were cared for in the Newborn Special Care Unit and survived to discharge were followed prospectively and evaluated with the same battery of developmental tests at 18 to 22 months corrected age. These data are submitted to the common NICHD Neonatal Research data center and are used to determine outcome which can be related to current newborn intensive care practices. (This is a NICHD Neonatal Research Network study. This is an observational study; therefore, there is not a defined number of patients expected for the entire study.)